1. Field of the Invention
The present invention relates to an organic EL device which is useful in display applications, and to a method of manufacturing such a device.
2. Background of the Related Art
In recent years, much research has been performed on organic EL devices using self-emissive organic EL elements for display applications. It is anticipated that organic EL devices will realize high emission luminance and emission efficiency. This is because high current densities can be realized at low voltages. In particular, commercialization of a multicolor emissive organic EL device with high fineness and capable of full-color display is anticipated in the field of display technology.
An important problem for commercialization of organic EL devices as color displays include, in addition to the realization of high fineness, is long-term stability, including color reproducibility. This is because multicolor emissive organic EL devices have the drawback that the emission characteristics (current-luminance characteristics) decline significantly as a result of driving over a constant period.
A representative cause of this decline in emission characteristics is the growth of dark spots. A “dark spot” is means an emission defect point. Such a dark spot is thought to occur due to the presence of oxygen and moisture in elements which cause the advancement of oxidation or agglomeration of material in a constituent layer of the organic EL element, during driving and during storage. Growth of a dark spot advances not only during the passing of current but during storage as well. In particular, dark spot growth is thought to be (1) accelerated by oxygen or water existing in the outer environment surrounding the element; (2) affected by oxygen or water existing in adsorbents in constituent layers; and (3) affected by water adsorbed onto components used in device manufacture or by intrusion of water during manufacture. If this growth continues, the dark spot may spread over the entire emissive face of the organic EL device.
In the prior art, methods in which metal cans and glass plates are used to seal organic EL elements, or methods in which a desiccant is arranged in the space in which an organic EL element has been sealed, have been employed as means of preventing intrusion of water into the constituent layers of organic EL elements. However, in order to exploit such features of organic EL devices as light weight and thin shape, techniques to use thin films for sealing, without using desiccants, are attracting attention.
As thin films for sealing, silicon oxide, silicon nitride, silicon oxide-nitride, and similar are used. For example, in Japanese Patent Application Laid-open No. 2001-176653 (Patent Reference 1), a film for sealing which uses silicon oxide is disclosed. However, silicon oxide is inferior with respect to permeability of oxygen and water, and so cannot suppress the occurrence of dark spots. In Japanese Patent Application Laid-open No. 2005-183147 (Patent Reference 2), a film for sealing which employs silicon nitride is disclosed. However, in Patent Reference 2 there is no disclosure of means for sealing particles or of means for suppressing the occurrence of cracks. Further, in Japanese Patent Application Laid-open No. 2005-285659 (Patent Reference 3) a film for sealing which employs SiH4, N2, and NH3 as reaction gases is disclosed. In Japanese Patent Application Laid-open No. 2004-63304 (Patent Reference 4), a film for sealing which employs SiH4, N2, and H2 as reaction gases is disclosed.
In an organic EL device, and in particular a device with a bottom-emission type structure, a color filter layer and CCM layer (color conversion layer) are formed on a glass substrate, and a planarization layer (overcoat layer) is formed using a polyimide silicon resin or another organic resin to bury the steps therein. Further, in order to prevent dispersion of residual water from this planarization layer into the organic EL layer, a passivation layer of SiO2, SiN, or similar is provided. Then, a transparent electrode of ITO, IZO or similar is formed into stripe shapes as anodes, and thereupon a cathode-separating layer with a reverse-taper shape is formed into stripe shapes perpendicular to the transparent electrodes. Then, the organic EL layer which is the emission layer is formed, and a reflective electrode of aluminum or similar is formed thereupon as a cathode. Because the organic EL layer which is the emission layer is extremely susceptible to oxygen and water, if air or water intrudes from portions which are peeled slightly or from defect portions of the cathode to reach the organic EL layer, growth of emission defect points such as DAs (Dark Areas) or DSes (Dark Spots) results. Further, there are concerns that the cathode (reflective electrode) may also be oxidized, and that conductivity and reflectivity may be worsened. Hence in general, in a chamber in which oxygen and water are suppressed to the extent possible, an absorbent and cover glass or another sealing substrate are sealed using ultraviolet-hardening epoxy resin or similar, to prevent intrusion of air and water. However, in a sealing method employing cover glass or another sealing substrate, the absorbent is inserted in a position opposing the organic EL device, and so such a method is not suited to organic EL devices having a top-emission type structure in which light is extracted from the upper portion.
This invention was devised in light of the above problems, and has as an object the provision of an organic EL device with excellent barrier properties with respect to water and oxygen, and which moreover can prevent degradation of the organic EL element, as well as a method of manufacturing such a device.